System of a dental blank and an associated shade guide

ABSTRACT

A system having at least one dental blank and an associated shade guide. The dental blank exhibits a non-uniform color shading, and the shade guide comprises a plurality of shade specimens each exhibiting a particular color shading representing the same color shading present in a partial area within the dental blank. A method of making a dental restoration includes the use of the system. The invention facilitates making a dental restoration having a color shading resembling the color shading of a natural tooth.

FIELD OF THE INVENTION

The invention relates to a system having a dental blank and anassociated shade guide, and in particular to a dental blank having anon-uniform color shading and a shade guide exhibiting shade specimensof the non-uniform color shading at different locations within thedental blank. The invention further relates to a method of making adental restoration by use of the system.

BACKGROUND ART

Dental restorations are often manufactured by an automated process,which typically includes:

-   -   capturing the shape of a patient's teeth, for example by        scanning a plaster model of the patient's teeth or alternatively        by scanning the actual teeth in the patient's mouth;    -   designing the shape of a dental restoration precursor based on        the captured shape using a computer-aided design (CAD) software;        and    -   machining the dental restoration precursor to correspond to the        designed shape, for example, by an automated Computer Numerical        Controlled (CNC) machine.

It is desirable that the dental restoration also has an appearance thatmatches or approximates the appearance of adjacent teeth. The appearanceof natural teeth is on the one hand provided by color shades, andfurther by a certain translucency. A dental technician or a dentalpractitioner, for example, typically selects the color of the ceramicmaterial to be used for the dental restoration according to the teeth ina patient's mouth that are located next to the tooth or teeth to berestored. For example, the appearance of relevant teeth in a patient'smouth may be determined using shade guides and the color shade for theframework and the veneer may be selected accordingly. Exemplary shadeguide types are available under the designations “VITA Classical ShadeGuide” or “VITA Toothguide 3D-Master®” from the company VITA ZahnfabrikH. Rauter GmbH & Co. KG, Germany. General types of materials for dentalrestorations are typically selected to meet certain mechanical andaesthetic requirements, which are for example the desired color and/ortranslucency.

Manufacturers of dental materials often offer dental restorativematerials in a variety of different color shades, and a dentaltechnician or a dental practitioner usually selects the shade of thematerial that is closest to the desired shade. Many approaches have beentried to provide dental restorative materials in color shades that matchthe desired color as closely as possible.

Although the current approaches for manufacturing of dental restorationsmay provide a variety of advantages, there is still a desire for amethod of manufacturing dental restorations in a reproducible, costefficient manner and at a good aesthetic quality.

SUMMARY OF THE INVENTION

The invention relates to a system which comprises at least one dentalblank and an associated shade guide.

The dental blank exhibits a non-uniform color shading in at least onedimension. Further the shade guide comprises a plurality of shadespecimens. Each of the shade specimens exhibits a specimen surface thathas a three-dimensional shape. Further each of the shade specimensexhibits a particular color shading defined by a virtualthree-dimensional target surface within the dental blank. The targetsurface has a shape which is equal to or which correlates to the shapeof the specimen surface.

The invention is advantageous in that it allows matching a non-uniformcolor shading, also sometimes referred to as “color gradient”, of adental restoration and a natural tooth color shading. The term“matching” as referred to herein thereby encompasses assimilation orapproximation, for example of colors. This means that for example a“matching” of colors or color shades does not require two matched colorsor color shades to be exactly identical. Further the invention allowsthe making of a variety of different non-uniformly color shaded dentalrestorations from the same type of non-uniformly color shaded blanks.The invention helps maximizing flexibility for a dentist or dentaltechnical in providing the dental restoration with a desired non-uniformcolor shading. Further the invention helps maximizing thereproducibility in the making of the dental restoration. For example theshade guide of the invention preferably provides unique information, forexample in the form of one unique encoding, for describing a non-uniformcolor shade of a tooth. This is in contrast to prior approaches in whichthe dental practitioner had to match different colors of the same toothwith different samples of a shade guide to landmark different colorcodes of the shade guide on a geometric diagram of that tooth.

In one embodiment the dental blank exhibits a non-uniform color shadingin two or all three dimensions. For example the non-uniform colorshading may be the same in all three dimensions or different in two orthree dimensions. A dental restoration obtained from such a dental blankmay relatively pleasantly resemble a natural tooth.

In one embodiment the shade guide is provided in the form of a physicalshade guide, having a holder allowing a user to hold the shade guideand, attached thereto, a number of physical shade specimens whichexhibit the particular non-uniform color shading. Such color shading isat least provided on the specimen surface. The shade guide thuspreferably allows presenting a plurality of different particularnon-uniform color shadings to a user. As described above each particularnon-uniform color shading is associated to an equivalent particularnon-uniform color shading in a dental blank. Such particular non-uniformcolor shading is preferably defined by the virtual target surface in aparticular position and orientation within the dental blank. Accordinglydifferent particular non-uniform color shadings can be defined bydifferent positions and/or different orientations of the target surfacewithin the blank. This is advantageous in that one type of a non-uniformcolor shaded blank can be used to make a variety of differently colorshaded dental restorations.

In a further embodiment the shade guide is provided in the form of avirtual shade guide, for example displayed on a computer screen. Thevirtual shade guide preferably has a number of virtual shade specimenswhich exhibit the particular non-uniform color shading. The virtualshade guide thus preferably allows presenting a plurality of differentparticular non-uniform color shadings to a user.

In a further embodiment the dental blank is made of differently coloredmaterials which in combination provide the dental blank with thenon-uniform color shading. Preferably the dental blank is“solid-colored”. This means for example that the non-uniform colorshading is provided in major volume portions of the dental blank, ratherthan just at an outer surface of the blank.

In one embodiment the three-dimensional shape of the specimen surface isnon-planar. In particular the three-dimensional shape of the specimensurface may correspond to a standardized shape of a human incisal tooth.This facilitates a comparison of color shades between the shadespecimens and a natural tooth by a user, for example a dentist, becausethis avoids that the same colors on differently shaped surfaces mayappear different.

In a further embodiment the dental blank further exhibits a non-uniformtransparency gradient in at least one dimension. Each shade specimen mayrepresent a particular transparency gradient present in the dental blankor obtainable from the dental blank adjacent the target surface withinthe dental blank. The non-uniform color shading and the non-uniformtransparency gradient may be combined in one blank.

Each specimen is preferably associated with a target surface of theinvention. The target surface preferably has a predetermined positionand orientation within the dental blank. The skilled person willrecognize that the target surface is virtual and refers to amathematical definition of a partial (virtual) cross-section having aposition and orientation within the dental blank. The non-uniform colorshading present at such partial cross-section is represented in oneshade specimen of the shade guide. Further in a pre-sintered blank thenon-uniform color shading defined by the target surface preferablyrefers to the same blank theoretically sintered to its final density.The target surfaces, as they are associated with different shadespecimens, have at least one of different positions and differentorientations in the dental blank.

In one embodiment the position of the target surface is defined by threecoordinates in a three-dimensional Cartesian coordinate system.Accordingly a particular position of the target surface may bedetermined by an X, Y and Z coordinate. Further the orientation ispreferably defined by a first inclination angle about a first axis, asecond inclination angle about a second axis and a rotation angle abouta third axis of the same Cartesian coordinate system. For example thefirst and second inclination angle may be determined by a rotation angleabout the Y-axis and Z-axis, respectively, of the coordinate system,whereas the rotation angle may be determined about the Z-axis. TheCartesian coordinate system which the position and orientation are basedon may have its origin at a pre-determined coordinate relative to orwithin the blank.

In one embodiment each specimen surface is assigned an encodingrepresenting information about the color shading and information aboutthe position and orientation of the target surface in the dental blank.Preferably the shade guide comprises such an encoding in the form ofvisible information. For example the encoding may comprise informationabout one or more colors present in the color shading and coordinates ofthe reference surface in the blank. Thus a user is enabled to read theencoding from the shade guide and for example communicate such encodingto a dental lab which manufactures the corresponding dental restoration.

In a further embodiment the dental blank is formed of a pre-sinteredceramic material having an open porous structure. In this embodiment thetarget surface may correspond to a proportionally enlarged shape of thespecimen surface. Accordingly the position and orientation of the targetsurface may include an offset. This is to account for a shrinkage of thedental blank during sintering toward its final density.

In an alternative embodiment the dental blank is formed of a solid blockof material (for example a glass ceramic material which is sintered toits final density or a dental composite material). In this embodimentthe target surface may be equal to the shape of the specimen surface.The dental blank may be formed for example of a dental compositematerial, for example LAVA™ Ultimate, as available from 3M DeutschlandGmbH, Germany. Further the dental blank may be formed of a dentalceramic, for example zirconia or glass ceramic, for example lithiumdisilicate.

In a further aspect the invention relates to a method of making a dentalrestoration. The method comprises the steps of:

-   -   providing a dental blank exhibiting a non-uniform color shading        in at least one dimension;    -   providing a shade guide that is associated to the dental blank,        the shade guide comprising a plurality of shade specimens each        exhibiting a specimen surface, wherein each specimen surface has        a three-dimensional shape and represents a particular color        shading defined by a virtual three-dimensional target surface of        a correlating shape within the dental blank;    -   visually matching one shade specimen of the shade guide with a        tooth of a patient and thereby determine a selected shade        specimen;    -   using a position and/or orientation associated with the specimen        and determining a correlating position and/or orientation within        the dental blank; and    -   machining the dental restoration, or a precursor thereof, at the        correlating position and/or orientation from the dental blank.

A precursor of the dental restoration may for example be machined from apre-sintered dental blank. Such a precursor is preferablythree-dimensionally proportionally enlarged relative to the dentalrestoration to account for shrinking during finally sintering. Aprecursor of the dental restoration may further be machined from or ablank made of a dental composite material.

In one embodiment the method further comprises the steps of:

-   -   determining the encoding associated with the selected shade        specimen; and    -   machining the dental restoration based on the encoding        associated with the selected shade specimen.        For example the encoding may be entered by a user or dental        practitioner in a machine for machining dental restorations.        Such a machine may be configured to retrieve or adapt a        machining program for machining the dental restoration at the        appropriate position and orientation as defined via the        encoding.

In one embodiment the method further comprises the steps of:

-   -   designing the dental restoration by computer aid based on a        virtual model of the dental restoration; and    -   using the target surface to determine the position and/or        orientation of the dental restoration, or the pre-cursor        thereof, within the dental blank.

The target surface and the dental restoration model may for example beput in a determined geometric relationship relative to each other, forexample on a CAD system by computer aid, so that by the position and/ororientation of the target surface relative to the blank the positionand/or orientation of the dental restoration relative to the blank isalso determined.

In a further embodiment the method further comprises the steps of:

-   -   capturing a color shade of a patient's tooth by taking an image        of the patient's tooth;    -   displaying the color shade of the patient's tooth on a computer;        and    -   providing the shade guide virtually on the computer.

The color shade may be captured by a photo camera, for example by aphoto camera of a smart phone or tablet computer, and an app on thesmart phone or tablet computer may provide a virtual shade guide fromwhich a user can select an appropriate shade specimen.

In a further embodiment the method comprises the steps of:

-   -   selecting a particular specimen for the color shade displayed on        the computer;    -   obtaining a position and orientation of the target surface in        the dental blank from the associated specimen; and    -   providing machine data for machining the dental restoration, or        a precursor thereof, from the dental blank.        For machining the dental restoration a dental milling or        grinding machine may be used.

Accordingly in a further embodiment the method comprises the steps of:

-   -   grinding the dental restoration from the dental blank; or    -   milling a precursor of the dental restoration from the dental        blank and sintering the precursor to form the dental        restoration.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of a dental blank according to anembodiment of the invention;

FIG. 2 is a front view on a shade guide according to an embodiment ofthe invention;

FIG. 3 is a cross-sectional view through a dental blank according to anembodiment of the invention;

FIG. 4 is a further cross-sectional view through a dental blankaccording to an embodiment of the invention;

FIG. 5 illustrates a dental restoration at different positions within adental blank according to an embodiment of the invention;

FIG. 6 illustrates a dental restoration at different inclinations withina dental blank according to an embodiment of the invention;

FIG. 7 illustrates a dental restoration at different rotations within adental blank according to an embodiment of the invention;

FIG. 8 illustrates the matching of a color shading using a physicalshade guide according to an embodiment of the invention;

FIG. 9 illustrates the matching of a color shading using a virtual shadeguide according to an embodiment of the invention;

FIG. 10 illustrates the design of a dental restoration based on thetarget surface according to the invention; and

FIG. 11 illustrates the design of FIG. 10 at a different design stage;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a dental blank 10 which has a non-uniform color shading.According to the invention the dental blank may be formed of severallayers each having a different color. Further the dental blank may nothave discrete and distinguishable color layers, but may have acontinuous non-uniform color shading, or may have similar or differentcolor shadings in two or all three dimensions of the dental blank. Forease of explanation the illustrated example refers to a dental blank inwhich the non-uniform color shading extends in one dimension only(vertical in the Figure). Further in this example the blank is formed offour distinguishable differently colored layers 11, 12, 13, 14. Thelayers 11-14 are arranged on top of each other and thus provide thedental blank 10 with the non-uniform color shading.

A target surface 20 is illustrated within the dental blank 10. Thetarget surface 20 is virtual and corresponds to a mathematicalrepresentation of a three-dimensional surface. The target surface 20 isentirely contained within boundaries of the dental blank 10. The virtualthree-dimensional target surface has a predetermined shape whichcorrelates to a shape of a specimen surface 31 a of a specimen 31 asshown in FIG. 2. The shape of the target surface 20 further approximatesthe shape of a tooth surface.

The example illustrates a cross-section 20′ through the dental blank 10in an area in which the virtual target surface 20 intersects with thedental blank 10. Accordingly a dental restoration cut out from thedental blank 10 in this area would essentially obtain the layerstructure as defined by the target surface 20. In particular such adental restoration would essentially obtain a color shading whichcomprises all four colors provided by the dental blank 10, however, onlysmall portions of the layers 11 and 14 would be present therein, whereasthe layers 12, 13 would extend entirely through the dental restoration.The skilled person will recognize that the target surface 20 is atwo-dimensional structure so that a three-dimensional dental restorationwould typically additionally also comprise cross-sections of a slightlydifferent layer structure. However—as further described in detailbelow—the target surface may be used to provide at least an outersurface of the dental restoration with the layer structure defined bythe target surface 20 or a similar layer structure.

FIG. 2 shows a shade guide 30 comprising a plurality of different shadespecimens 31-36. The shade specimens 31-36 in the example have the samethree-dimensional shape, but exhibit different specimen surfaces 31 a-36a. In particular each of the specimen surfaces 31 a-36 a represents aparticular color shading. For example the color shading represented bythe specimen surface 31 a is defined by a virtual three-dimensionaltarget surface (shown as item 20 in FIG. 1). The target surface 20(virtually located) within the blank 10 corresponds in shape with theshape of the specimen surface 31 a. It is noted that in case the dentalblank is formed of a pre-sintered porous material the target surface 20may be proportionally enlarged with respect to the specimen surface 31a. This is because such dental blank 10 typically has an open-celledstructure and a dental restoration obtained from such blank has to beproportionally oversized to account for shrinking during sinteringtoward a solid structure.

FIG. 3 and FIG. 4 are schematic illustrations of a cross-section throughthe blank 10 and a target surface 20 in different positions and/ororientations. As shown the target surface 20 in FIG. 3 relative to FIG.4 defines different particular color shadings depending on the positionand/or orientation of the target surface 20 within the blank. The targetsurface 20 has a position P relative to a blank reference coordinate Rwithin the dental blank 20. The position of the target surfacepreferably relates to a pre-determined target reference coordinate P onor relative to the target surface. For example such target coordinate Pmay be determined at the lower right corner (see FIG. 1) of the targetsurface 20. The skilled person will however recognize that the targetcoordinate P may be pre-determined at any other appropriate locationrelative to the target surface 20 as long as the relation betweencoordinates defining the target surface 20 and the target coordinate isdefined. Further the target surface 20 has an orientation relative to areference axis X or Y within the dental blank 20. The orientation of thetarget surface 20 preferably relates to a pre-determined targetreference axis A on the target surface 20. For example the targetreference axis A may be determined as a tangent on the target surface 20through the target coordinate P. The skilled person will howeverrecognize that such target reference axis A may be pre-determined at anyother appropriate orientation relative to the target surface 20 as longas the relation between coordinates defining the target surface 20 andthe target reference axis is defined. It is noted that the orientationof the target surface is further defined by axes B and C which arearranged in a perpendicular relationship to each other and to the axisA. These two further axes are however omitted for better clarity in thetwo-dimensional illustration of the example.

As demonstrated by FIG. 3 and FIG. 4 different particular color shadingsof the target surface can be provided by simply moving and/or orientingthe target surface within the dental blank. In FIG. 3 for example thetarget surface 20 defines a color shading having four different colors,whereas the same target surface 20 just positioned and orienteddifferently defines a color shading having only two different colors. Inthe latter case further the two colors shown in FIG. 4 extend overlarger portions of the target surface 20 than the same colors in FIG. 3.Therefore a multiplicity of equally color shaded dental blanks cannevertheless be used to provide a wide variety of differently colorshaded dental restorations.

Accordingly the shade guide 30 as shown in FIG. 2 preferably has aplurality of specimen surfaces each associated with a target surface atone of a plurality of different positions and orientations. For examplethe specimen surface 31 a in FIG. 2 may have the same shape as thereference surface 20 in FIGS. 3 and 4 and may be associated with aposition and orientation of the target surface 20 as shown in FIG. 3. Onthe other hand the specimen surface 32 a in FIG. 2 may be associatedwith the same target surface 20 but at a different position andorientation within the dental blank.

FIG. 5 shows a (virtual) dental restoration 40 at the same orientationbut at different positions within the blank 10. As shown the colorshading of the dental restoration 40 depends on the position of thedental restoration 40. To determine the position of a dental restoration40 within the blank 10 in a first step the shade guide may be used todetermine a particular color shading. Because the specimens of the shadeguide are associated with a target surface at a particular positionwithin the dental blank 10 the associated target surface can in afurther step be used to define the position of a surface of the dentalrestoration 40 and thus of the dental restoration 40 itself. The surfaceused for positioning the dental restoration 40 preferably corresponds toan outer visible surface of the final dental restoration, particularlysuch surface which is intended to obtain the color shading initiallydetermined by the shade guide.

FIGS. 6 and 7 illustrate that the dental restoration may further havedifferent inclination angles (FIG. 6) and/or different rotation angles(FIG. 7). FIG. 6 shows different inclinations in only one dimension,however, the skilled person will recognize that further inclinations arepossible in a further dimension (perpendicular to the plane of theFigures). Thus the invention allows the making of a variety ofdifferently color shaded dental restorations by machining the dentalrestorations at different positions and or orientations from equallycolor shaded dental blanks.

The skilled person will recognize the instead or in addition to a colorshading the blank may have a transparency gradient. Accordingly what isdescribed for the color shading identically applies for any transparencygradient of the dental blank and/or the dental restoration.

In the following the method of making the dental restoration isexplained in further detail.

FIG. 8 illustrates the visual matching of a shade specimen of the shadeguide 30 with a tooth 100 of a patient. In the example a user, forexample a dentist, uses a physical shade guide and positions a shadespecimen it next to a patient's tooth 100 to be restored. The usertypically compares the color shading of different shade specimens withthe actual color shading of the patient's tooth and selects the shadespecimen which matches best. The skilled person is aware that the samematching step can be performed with one of the neighboring teeth of thepatient's tooth to be restored, for example in case the tooth to berestored is missing or otherwise unsuitable or unavailable for colormatching.

Each shade specimen of the shade guide 30 is associated with apredetermined position and orientation of a (virtual) target surface ina (virtual) dental blank. Accordingly the shade guide may have a codefor each shade specimen that represents or allows obtaining theassociated predetermined position and orientation within the dentalblank. Further the shade guide and/or the shade specimens may beassociated with a certain type of color shaded dental blank, so that fordifferently color shaded blanks further shade guides and/or shadespecimens may be available. Therefore the code may further compriseinformation about the type of dental blank which the shade guide andshade specimen is associated with.

FIG. 9 shows the matching of a virtual shade specimen 50 with a tooth100 of a patient. In the example a user, for example a dentist, uses animage of the patient's teeth in combination with a computer simulated orvirtual shade guide. The image may be taken real time, for example via alive camera, or in advance of the matching, for example by a photocamera. Such image is preferably visualized to the user on a screen of acomputer. The computer may have implemented a virtual shade guidecomprising a plurality of differently color shaded shade specimens.Further the computer may provide for a switching option allowing a userto switch between different shade specimens. In the example a shadespecimen 50 is displayed besides the tooth to be restored 100 in anoverly of the shade specimen 50 on the image. The user may accept thespecimen 50 by a user input or switch to and accept another specimenstored in the computer, and thereby perform the matching. The computermay further have functionality to measure the degree of the matchingbetween the tooth and a certain specimen, for example by a statisticalcomparison of the color distribution on the tooth relative to the shadespecimen. Further the computer may have functionality to propose acertain shade specimen based on a color measurement of the patient'stooth or the image of the patient's tooth.

In this example the computer preferably has stored information about theshade specimens and the associated position and orientation of thetarget surface within the blank. Preferably position and orientation ofthe target surface within the blank is automatically determined uponselection of a shade specimen.

FIG. 10 and FIG. 11 illustrate—for better clarity in a two-dimensionalview only —one way of using the target surface according to theinvention to create a dental restoration. In particular a target surface20 is provided virtually, for example in the form of a three-dimensionalcomputer representation within a (dental) CAD system. The target surface20 has a standardized shape approximating an outer tooth surface (forexample a labial surface of a human average incisal tooth). Further athree-dimensional computer representation of the dental restoration isprovided within the CAD system. Such a virtual dental restoration may beobtained from designing by a user. For designing a dental restoration,typically at least part of a patient's dentition is captured (forexample scanned) and the captured data is provided to the CAD system inthe form of a three-dimensional computer representation. Based on thisthe user may design a restoration of a tooth to be restored. The CADsystem may have a database from which certain standard tooth shapes maybe retrieved, and a user may adapt such a standard tooth shape inaccordance to the geometric situation of the patient's dentition. Or theuser may design the entire restoration by use of CAD software tools,accounting for the geometric limitations present in the patient'sdentition.

The CAD system preferably allows a user to three-dimensionally move androtate the target surface 20 and the dental restoration relative to eachother. Accordingly the user may manually combine the target surface 20and a surface of the dental restoration 60 as illustrated in FIG. 11.However the CAD system may further have functionality to determine anaverage orientation of the surface of the dental restoration 60 andadapt the orientation of the target surface accordingly. Further the CADsystem may further have functionality to automatically combine thetarget surface 20 and the surface of the dental restoration 60 so thatthe target surface 20 and the surface of the dental restoration 60intersect.

The target surface 20 being selected by the shade guide of the inventionis preferably associated with a shade specimen of the shade guide andthus with a position and orientation within a color shaded dental blank.Accordingly such position and orientation associated with the specimenmay be used to determine a correlating position and orientation withinthe blank. Because target surface 20 is combined with the virtual dentalrestoration 60 (and thus the target surface 20 and the virtual dentalrestoration 60 are in a determined geometric relationship) the dentalrestoration can be machined out of the blank at a position andorientation as associated with the target surface 20. Thereby theposition and orientation is preferably a relative position andorientation from a reference position and reference orientation of theblank.

The position and orientation associated with the target surface ispreferably transmitted to a device for machining the dental blank, forexample a milling machine. The dental restoration, or a precursorthereof, can then be machined from the dental blank at the correlatingposition and/or orientation. It is noted that in case a pre-sintereddental blank is used the position and orientation associated with thetarget surface may include an offset at least in dimensions defining theposition. This is to account for any shrinkage resulting from sinteringthe blank or restoration precursor toward the final density.

The invention claimed is:
 1. A method of making a dental restoration,the method comprising: providing a dental blank exhibiting a non-uniformcolor shading in at least one dimension; providing a physical shadeguide that is associated to the dental blank, the physical shade guidecomprising a plurality of physical shade specimens each exhibiting aspecimen surface, wherein each specimen surface has a three-dimensionalshape and a particular non-uniform color shading defined by a respectivevirtual three-dimensional target surface of a correlating shape andnon-uniform color shading within the dental blank, and wherein each ofthe respective virtual three-dimensional target surfaces has a shapecorresponding to the corresponding specimen surface; storing, by acomputing device, information associating each of the plurality ofphysical shade specimens with respective positions and orientations ofvirtual three-dimensional target surfaces; matching one physical shadespecimen of the physical shade guide with a tooth of a patient andthereby determine a selected physical shade specimen; determining, by acomputing device and based on the selected physical shade specimen andthe stored information, a correlating position and orientation withinthe dental blank of the respective virtual three-dimensional targetsurface associated with the selected physical shade specimen, whereindetermining the correlating position and orientation within the dentalblank comprises automatically combining the target surface and a surfaceof a virtual dental restoration so that the target surface and thesurface of the virtual dental restoration intersect at an intersection;and machining the dental restoration, or a precursor thereof, at thecorrelating position and orientation from the dental blank based on theintersection of the target surface and the surface of the virtual dentalrestoration.
 2. The method of claim 1, wherein each specimen surface isassigned an encoding representing information about the non-uniformcolor shading and information about the position and orientation of thetarget surface in the dental blank, the method further comprising:determining the encoding associated with the selected physical shadespecimen; and machining the dental restoration based on the encodingassigned to the selected physical shade specimen.
 3. The method of claim1, further comprising: designing the dental restoration by computer aidbased on the virtual dental restoration.
 4. The method of claim 1,wherein machining the dental restoration, or a precursor thereof,comprises: grinding the dental restoration from the dental blank.
 5. Themethod of claim 1, wherein machining the dental restoration, or aprecursor thereof, comprises milling a precursor of the dentalrestoration from the dental blank and sintering the precursor to formthe dental restoration.
 6. The method of claim 1, wherein matching theone physical shade specimen comprises matching, by a computing device,the one physical shade specimen based on a comparison of a colordistribution on the tooth relative to one or more of the plurality ofshade specimens.